1. Field of the Invention
This invention relates to methods of image processing, particularly methods of comparing images.
2. Prior Art
Computer image processing techniques have created new methods to enhance, analyze, and compare images, particularly X-ray images. Computers can, for example, compare two images obtained by X-ray before and after an X-ray contrast agent is administered, or a first image of an artery taken during systole and a second taken during drastole.
Computers have also allowed the generation of two-dimensional images of "slices" through the interior of three-dimensional objects. Two methods used in medicine for obtaining images that represent "slices" through the human body are X-ray computer tomography (hereinafter "CT") and nuclear magnetic resonance imaging (hereinafter "MR").
The images obtained from CT and MR are extremely useful to a diagnosing physician. Interior regions of the body not normally accessable, except by surgery, can be seen for diagnostic purposes. As the resolution of the techniques improve, more internal structure is shown. Unfortunately, the structure shown in some areas of the body, particularly the brain, is so complex that no physician can be expected to remember the identity and functions of every part of the structure shown. To solve the memory problem, physicians frequently refer to text books of reference images where the features of similar images are identified. This solution is unsatisfactory for several reasons: the physical book must be nearby for use as the physician is operating the computer console; the book may not show the exact series of images the physician desires; and the images in a book cannot be easily updated as new information becomes available.
It would be advantageous to have a system that provides the information found in a textbook in a computer data base. Then, the patient's image could be compared to the reference image at the terminal. Text, regarding specific areas of an image could be obtained to refresh the physican's memory. Furthermore, manipulations of the patient's image could be duplicated on the reference image.
The system of this invention allows the analysis of a working image by comparing it to a previously obtained reference image. Other sorts of images that may be analyzed include micropictographs and image from satellites, for example LANDSAT.